When an entity is enqueued without preempting current, we must ensure
that the slice protection is updated to take into account the slice
duration of the newly enqueued task so that its lag will not exceed
its slice (+ tick).

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/fair.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 85238f2e026a..d815609526d5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -889,12 +889,12 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
  * When run to parity is disabled, we give a minimum quantum to the running
  * entity to ensure progress.
  */
-static inline void set_protect_slice(struct sched_entity *se)
+static inline void set_protect_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	u64 quantum;
 
 	if (sched_feat(RUN_TO_PARITY))
-		quantum = cfs_rq_min_slice(cfs_rq_of(se));
+		quantum = cfs_rq_min_slice(cfs_rq);
 	else
 		quantum = normalized_sysctl_sched_base_slice;
 	quantum = min(quantum, se->slice);
@@ -905,6 +905,13 @@ static inline void set_protect_slice(struct sched_entity *se)
 		se->vprot = se->deadline;
 }
 
+static inline void update_protect_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
+{
+	u64 quantum = cfs_rq_min_slice(cfs_rq);
+
+	se->vprot = min_vruntime(se->vprot, se->vruntime + calc_delta_fair(quantum, se));
+}
+
 static inline bool protect_slice(struct sched_entity *se)
 {
 	return ((s64)(se->vprot - se->vruntime) > 0);
@@ -5468,7 +5475,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 		__dequeue_entity(cfs_rq, se);
 		update_load_avg(cfs_rq, se, UPDATE_TG);
 
-		set_protect_slice(se);
+		set_protect_slice(cfs_rq, se);
 	}
 
 	update_stats_curr_start(cfs_rq, se);
@@ -8730,6 +8737,9 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
 	if (__pick_eevdf(cfs_rq, !do_preempt_short) == pse)
 		goto preempt;
 
+	if (sched_feat(RUN_TO_PARITY) && do_preempt_short)
+		update_protect_slice(cfs_rq, se);
+
 	return;
 
 preempt:
-- 
2.43.0

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     3a0baa8e6c570c252999cb651398a88f8f990b4a
Gitweb:        https://git.kernel.org/tip/3a0baa8e6c570c252999cb651398a88f8f990b4a
Author:        Vincent Guittot <vincent.guittot@linaro.org>
AuthorDate:    Tue, 08 Jul 2025 18:56:29 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 09 Jul 2025 13:40:23 +02:00

sched/fair: Fix entity's lag with run to parity

When an entity is enqueued without preempting current, we must ensure
that the slice protection is updated to take into account the slice
duration of the newly enqueued task so that its lag will not exceed
its slice (+ tick).

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250708165630.1948751-6-vincent.guittot@linaro.org
---
 kernel/sched/fair.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 45e057f..1660960 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -889,13 +889,13 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
  * When run to parity is disabled, we give a minimum quantum to the running
  * entity to ensure progress.
  */
-static inline void set_protect_slice(struct sched_entity *se)
+static inline void set_protect_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	u64 slice = normalized_sysctl_sched_base_slice;
 	u64 vprot = se->deadline;
 
 	if (sched_feat(RUN_TO_PARITY))
-		slice = cfs_rq_min_slice(cfs_rq_of(se));
+		slice = cfs_rq_min_slice(cfs_rq);
 
 	slice = min(slice, se->slice);
 	if (slice != se->slice)
@@ -904,6 +904,13 @@ static inline void set_protect_slice(struct sched_entity *se)
 	se->vprot = vprot;
 }
 
+static inline void update_protect_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
+{
+	u64 slice = cfs_rq_min_slice(cfs_rq);
+
+	se->vprot = min_vruntime(se->vprot, se->vruntime + calc_delta_fair(slice, se));
+}
+
 static inline bool protect_slice(struct sched_entity *se)
 {
 	return ((s64)(se->vprot - se->vruntime) > 0);
@@ -5467,7 +5474,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 		__dequeue_entity(cfs_rq, se);
 		update_load_avg(cfs_rq, se, UPDATE_TG);
 
-		set_protect_slice(se);
+		set_protect_slice(cfs_rq, se);
 	}
 
 	update_stats_curr_start(cfs_rq, se);
@@ -8720,6 +8727,9 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int 
 	if (__pick_eevdf(cfs_rq, !do_preempt_short) == pse)
 		goto preempt;
 
+	if (sched_feat(RUN_TO_PARITY) && do_preempt_short)
+		update_protect_slice(cfs_rq, se);
+
 	return;
 
 preempt: